WASHINGTON, Feb 5 (Reuters) - The Obama administration enlisted the help of First Lady Michelle Obama in an effort to ensure that low- and middle-income families get access to federal aid to help them pay for college.

She urged students and their parents on Wednesday to take advantage of a form known as the Free Application for Federal Student Aid, or FAFSA. The form is used to determine eligibility for the different types of financial aid, including grants, loans and federal work-study programs.

"Unfortunately, too many students don't even bother to apply for college because they don't think they'll ever be able to afford it, and so they just walk away from the opportunity without getting any advice or seeking any support," Obama told students at T.C. Williams High School in Alexandria, Virginia.

Obama, who has often spoken of how she relied on student loans to pay for her undergraduate education at Princeton University, said she filled out the FAFSA form with the help of her mother, and worked at a daycare center while in college through the work-study program.

She urged the students to work with their parents and teachers to fill out the forms as early as possible.

The effort to boost applications for college financial aid is part of a domestic policy agenda President Barack Obama unveiled in his State of the Union address last month that focuses on boosting upward mobility in the U.S. economy.

Last year, only half of the country's high school seniors filled out the FAFSA form, according to the Department of Education. Many of those who did not were from poor families.

Higher education experts have said the complexity of the financial aid process discourages many eligible students and families from applying.

"There is compelling evidence that getting help with that form and filing the FAFSA can increase college attendance," said William Doyle a professor of public policy and higher education at Vanderbilt University who has written about FAFSA. "It's particularly important to establish early the awareness of financial aid."

Education Secretary Arne Duncan, who also attended the event, said his department tried to streamline the application process by cutting down the number of questions on the form and by using a tool that retrieves financial information from applicants' tax returns.

Duncan said that he hoped some day to eliminate FAFSA forms and instead switch to a system based on tax returns.